Researchers found a three-fold increase in the odds of hip fracture for HbA1c levels below 6% relative to levels above 8%; for HbA1c levels between 6% and 7%, the odds of fracture were doubled….

Dr. Troy H. Puar from Changi General Hospital and colleagues noted that, while a greater risk of falls in older adults with tight glycemic control has been noted previously, "this is the first study showing an association between tight glycemic control and hip fractures in older adults with type 2 diabetes."

According to the researchers, longitudinal studies are needed to confirm the link between fractures and glycemic control. But in the meantime, they think physicians "need to exercise greater caution when treating older adults with diabetes mellitus."

"We believe that older people with diabetes should still receive optimal control of their diabetes (which is HbA1C of < 7% as most guidelines suggest) as long as they are not experiencing episodes of hypoglycemia secondary to treatment," Dr. Puar noted.

"Particularly, use of insulin and sulphonylureas are well known to cause hypoglycemia, and in our study as well, they were shown to be widely used amongst patients with hip fractures. On the other hand, medications such as metformin and acarbose were protective, which may be due to (their) ability to lower glucose levels without causing hypoglycemia," Dr. Puar said.

Treatments need to be individualized: for instance, in an older patient with higher risk of falls and hypoglycemia, currently on insulin or sulphonylurea, with glycemic control well within target range, the clinician should consider switching the patient to medications that do not cause hypoglycemia such as metformin.

Dr. Puar and colleagues note that because older adults are more prone to hypoglycemic episodes and subsequent falls, the American Geriatrics Society recommends a less-stringent HbA1c target of 8% or less in frail older adults or those with a short life expectancy.

Their study included 558 elderly people (mean age, 77 years) with type 2 diabetes seen at Changi General Hospital between 2005 and 2010 for hip fracture. Each case was matched to one control for sex, age, race, duration of diabetes and comorbidities. Roughly three-quarters of cases and controls were women.

The researchers say cases had a significantly lower median HbA1c level (6.8%) than controls (7.4%); in 59.2% of cases HbA1c was less than 7% and 75.4% were undergoing treatment with sulfonylureas.

Multivariate analysis adjusting for age, sex, race, comorbid conditions, and other confounders confirmed that subjects with lower HbA1c were at higher risk of breaking a hip. The odds ratio was 3.01 for people with HbA1c levels below 6% vs. those with HbA1c levels greater than 8% (p<0.001). Those with HbA1C levels between 6.1% and 7% were also at greater risk with an OR of 2.34 (p<0.001).

A similar number of cases and controls used sulfonylureas and insulin. Treatment with metformin or acarbose was associated with a significantly lower risk of fracture (OR, 0.73 and 0.54, respectively).

Another possibility that might help explain the increased hip fracture risk with lower HbA1c is bone density, Dr. Schwartz said, noting that in a recent meta-analysis HbA1c was positively correlated with bone density.

Their findings were published online August 2, 2012 in the Journal of the American Geriatrics Society (JAGS).